Research Note Reduction of sediment, phosphorus and nitrogen transport on vegetated buffer strips Jaana Uusi-Kämppä and Toivo Yläranta Uusi-Kämppä J. & Yläranta, T. 1992. Reduction of sediment, phosphorus and nitrogen transport on vegetated buffer strips. (Research Note). Agric. Sei. Finl. 1: 569-575. (Agric. Res. Centre of Finland, Inst. Soils and Environ., SF-31600 Jokioinen, Finland.) The largest source of phosphorus and nitrogen in surface waters is cultivated soils. The effects of ten-meter wide grass buffer strips (CBS) on sediment and nutrient losses from cropped soil plots have been studied forone year at the Agricultural Research Centre in Finland. The GBS plots were compared to plots without vegetated buffer strips (no- VBS). The GBSs decreased loads of total solids, phosphorus and nitrogen by an average of 23, 6 and 47%, respectively. The grass buffer strips were effective in autumn but not in spring. Thirty-eight percent more soluble phosphate phosphorus was leached from the GBS plots than from the plots without GBSs, because of their inefficiency in spring. Key words: water erosion, grass buffer strip, non-point pollution, runoff Introduction In Finland, the relative importance of non-point pollution has increased during the last two decades. The most important nutrients carried to surface wa- ters are phosphorus and nitrogen. At present, agri- culture contributes most of the diffuse loading (Rekolainen 1989). Phosphorus is the main nutrient limiting primary production in Finnish lakes. Experimental results have indicated that 75% of the phosphorus trans- ported to watercourses is bound to sediment, and about 5% of the sediment-bound phosphorus is available for algal growth (Ekholm et al. 1991). In total, 29% of the phosphorus load (soluble + ad- sorbed) is biologically available (EKHOLM 1992). As a result of these findings, methods that de- crease phosphorus and nitrogen losses from agri- cultural land are of increasing interest in Finland. These methods include cultivation practicies and vegetated buffer strips, i.e. uncultivated areas be- tween fields and watercourses. Permanent vegeta- tion on the strip protects the river bank from erosion and leaching (Ahola 1990). In the United States of America, buffer strips have been shown to be effec- tive for the removal of sediment and other sus- pended solids from surface runoff if the flow is shallow and uniform (Magette et al. 1987, Die- laha et al. 1989). Since 1991 the influence of various vegetated buffer strips on nutrient loss from fields into water- courses has been studied at the Agricultural Re- 569 Agric. Sei. Fin!. 1 (1992) https://www.c-info.fi/en/info/?token=R3UiX61MiS4DkRQF.z1ih50iNyhtiY3vGZ1B79w.C9-FT2C_aIr7BQys7PL5f7Sl3-QQPAoVPkbNbE1cGDI_Wh989SbOkFrNW7iw4_FZXdlvO1E06ibfTEYAFKyNfuX9RtSFPUlh36ZDC41yregQV7iZIETn_RBpH_B-Gqo6lDSviu6lfqh22DV8TvLJDdyK5itcqwISaDVdDyouJFt7waPLVz33oPe3_t122nEfLlEwjjfMwVJuuBk3Tif76r5AXLqEyEYq-zAtCfw8qLXNqkLQPbOk54H9zSBySHdvUfu-BtGY6eSmgFDqPS98Thg8APKgzdM0qVhawXMXOuR0piqn4PenoRMt search Centre of Finland. This paper presents the experimental results from the first year. Material and methods Experimental field A 6-plot experimental field was established at the Agricultural Research Centre in Jokioinen, south- ern Finland (60° 48’ N and 23° 28’ E) during the autumn of 1989. The soil on the experimental field contains 54-63 per cent clay (particle size < 0.002 mm) in the plough layer (0-20 cm). The ten-meter broad buffer strips are situated below the cropland source area (Fig. 1) which is flat, but the buffer strips are on a slope of 16%, varying between 12% and 18%. The experimental treatments were as follows (two replicates): 1) spring grain and a 10 m wide grass buffer strip sown with timothy (Phleum pratense ) and meadow fescue (Festuca pratensis) (GBS); 2) spring grain and no vegetated buffer strip (no- VBS); 3) spring grain and a 10 m wide vegetated buffer strip where typical Finnish bushes, hardwood trees, and wild hay and flowers are growing (VBS). Before the experiment the field was calibratedfor one year by cultivating plots in the same way and collecting water and soil samples. The loads of runoff, total solids and nutrients varied between the plots. The differences were considered when the experiment was being established and the buffer strips were being sown on the plots (Fig. I). Surface and subsurface water to a depth of 30 cm flowed into one collector trench on each plot. The volume was measured and a representative sub- sample was taken for laboratory analysis. Water sampling and analysis Water samples of500 ml were collected in polyeth- ylene bottles once a week or every second week during the runoff time. Total solids, and concentra- tions of total nitrogen and total phosphorus were determinated in unfiltered samples. For other deter- minations, samples were filtered through a mem- brane filter (Sartorius 11306-50-PFN, pore size 0.45 pm) before analysis. Total solids were determined as evaporated resi- due after drying at 105°C. Total phosphorus, sol- uble phosphate phosphorus, total nitrogen, nitrate nitrogen and ammonium nitrogen were analyzed according to the Finnish standard methods (SFS 3026, SFS 3025, SFS 3031, SFS 3030 and SFS 3032) and using Flow Injection Analysis on a LACHAT QuikChem analyzer. Results Surface and subsurface runoff did not vary much between plots during the calibration and experi- mental periods (Table 1). Precipitation during the period when runoff oc- cured was (Ilmatieteen laitos 1990, 1991, 1992): -calibration year 1990/91 (2.8.1990-16.5.1991) 460 mm - experimental year 1991/92 (25.9.1991- 21.4.1992) 354 mm. In the experimental year, the plots without the vegetated buffer strips (no-VBS) were compared only with the grass buffer strip (GBS) plots (Table 1). The plots with bushes and trees (VBS) were omitted from the comparison because the strips were poorly covered by vegetation and did not function properly. Total solids The loads of total solids varied over all the plots from 270 to 530 kg/ha during the calibration and experimental years (Table 1). In the autumn of 1991, the load of total solids from the GBS plots 570 Research NoteAgric. Sei. Fin!. 1 (1992) 2 was 170 kg/ha, only 51% of that from the no-VBS plots. However, in the spring the loss of suspended material from the GBS plots was 240 kg/ha, 20% greater than that from the no-VBS plots. Consider- ing the whole experimental year, the GBSs de- creased total solids in the runoff water by an aver- age of 120 kg/ha (23%). Phosphorus losses The loads of total phosphorus and soluble phos- phate phosphorus were almost the same on all plots during the calibration period (Table 1). During the first experimental year phosphorus losses were greater than during the calibration period; the total load was more than doubled on the no-VBS plot. Fig. I. Schematic diagram of experimental field. 571 Agric. Sei. Fint. 1 (1992) Research Note Table I. Loads of surface and subsurface runoff (Total runoff), total solids (TS) and nutrients during calibration and experimental periods. Period Plots Treat- Total TS Tot-N NOa-N NH4 +-N Tot-P PO-t’-P ments runoff (mm) (kg/ha) Calibration Autumn 1990 19 150 3.5 3.2 0.03 0.14 0.02 Spring 1991 1 no-VBS 44 220 2.8 2.4 0.09 0.16 0.04 Sum 1990/91 63 370 6.3 5.6 0.12 0.30 0.06 Calibration Autumn 1990 15 100 3.0 2.8 0.02 0.10 0.02 Spring 1991 2 no-VBS 39 170 2.9 2.5 0.07 0.12 0.04 Sum 1990/91 54 270 5.9 5.3 0.09 0.22 0.06 Experimental Autumn 1991 15 170 0.5 0.3 0.01 0.20 0.02 Spring 1992 I GBS 61 240 1.9 1.4 0.10 0.27 0.09 Sum 1991/92 76 410 2.4 1.7 0.11 0.47 0.11 Experimental Autumn 1991 16 330 2.0 1.4 0.02 0.30 0.02 Spring 1992 2 no-VBS 43 200 2.5 2.1 0.06 0.20 0.06 Sum 1991/92 59 530 4.5 3.5 0.08 0.50 0.08 Whilst losses from the GBS plot were greater than those in the calibration period, the buffer strip ap- peared to reduce total phosphorus load by 6% over- all, comprising a reduction in the autumn of 100 g/ha (33%), but an increase in the spring of 70 g/ha (35%). On the GBS plots 23% oftotal phosphorus was in the form of phosphate, but on the no-VBS plots only 16% was phosphate phosphorus. The losses of soluble phosphate phosphorus were 38% greater from the GBS plots than from the no-VBS plots, solely because of the much greater (by 30 g/ha or 50%) loss from the GBS plots in spring. Nitrogen losses During the experimental period less total nitrogen was leached than during the calibration period. Even the no-VBS plots lost 1.4kg N/ha less, but the GBSs reduced losses over the previous year by 3.9 kg N/ha and over the no-VBS plots by 2.1 kg N/ha. One reason for the reduced loss from the no-VBS plots may be that the 10m wide area in the slope of even the no-VBS plots was withoutany plant cover during the calibration year and the year before that. Obviously, quite a lot nitrogen had been mineral- ized during the two years and so any nitrogen mov- ing through the strips was well-utilized. Buffer strips also reduced nitrate losses. The load of nitrate nitrogen from the GBS plots (1.7 kg/ha) was only halfof that from the no-VBS plots (Table 1). In autumn 1991 load of nitrate nitrogen from the GBSs (0.3 kg/ha) was over four times smaller than from the no-VGB plots. In spring 1992 the loads were higher, but difference between plots became smaller. Loads of ammonium nitrogen were very small, and varied from 80 g/ha on the no-VBS plots to 572 Agric. Sei. Fint. 1 (1992) Agric. Sei. Fint. 1 (1992) 1 10g/ha on the GBS plots in the experimental year. This was because a small autumn benefit from GBSs was affect by a much larger negative effect in spring. Discussion In this experiment the loads of total solids were small. Puustinen (1992) found loads of total solids three times larger on an experimental field near Turku in southwesternFinland during winter 1990- 1991. In that research the runoff was also three times larger than in this experiment. Mansik- kaniemi (1982) studied stream systems in south- western Finland and, compared to this research, found ten times the amount of material (4000-4500 kg/ha) washed out from undulating arable land in a dry year. The small loss of total solids in this ex- periment was caused by the flatness of the experi- mental field which resulted in very little runoff. Losses of phosphorus were also small in this study. Puustinen (1992) found 6-7 times more total phosphorus in surface and subsurface waters only 70 km southwest of Jokioinen on similar soil, and Turtola and Jaakkola (1985) found a little more phophorus in surface waters from cropland in Jokioinen. In this study the amounts of total phos- phorus lost were small because most phosphorus was bound to soil particles and there was not much erosion from the field. Loads of nitrogen and nitrate nitrogen from the no-VBS plots were almost the same as those from cropland areas found by PUUSTINEN (1992) and Turtolaand Jaakkola (1985). On the GBS plots the loads of nitrogen were smaller than in the other experiments in Finland. DILLAHA et al. (1989) found that in Virginia in the USA 9.1 m wide vegetated filter strips on 11% and 16% slopes decreased sediment and total phos- phorus losses from bare cropland by an average of 84 and 79%, respectively. In Maryland, Magette et al. found reductions in losses of sediment and total phosphorus by 9.2 m wide vegetated filter strips of 86 and 53%, respectively, from a fallowed field. In this study only the effect on nitrogen losses (47%) was almost as large as in the USA. Decreases in losses of total solids (23%) and total phosphorus (6%) were much smaller. There are four possible reasons for this. Firstly this study was carried out without irrigation, whereas in the USA a rainfall simulator was used to apply 100 mm ofrainfall to each plot over a two-day period. A rainfall intensity of 50 mm/h was used during all simulations. Secondly, the climate inFinland is very different from that in Virginia and Maryland. Here the soil was covered by snow in the winter. Thus, the vege- tation on the GBSs did not grow during the period of main runoff in the early spring, in contrast to the sitution in the USA where the filter strips were effective throughout the whole experimental pe- riod. Thirdly, in the USA cropland source area was fertilized and left bare before rainfall simulations. In this experiment source area was sown with bar- ley which took nutrients from the soil during sum- mer. Forthly, the particle size distribution of the soil in these experiments was different. The Finnish soil was finer with much more clay. In this experiment soluble phosphate phosphorus leaching increased 50% from the GBSs in the spring. Dillaha et al. (1989) found that phosphate yields from buffer strips were often larger than the inputs to the buffers. They also indicated that there was a tendency for previously trapped phosphorus to be released from the buffer strip vegetation and soil as soluble phosphorus during later runs. In Finland Turtola (1990) found that leaching of soluble phosphate phosphorus increased from green fallow field during the second year of an experiment because of phosphate loss from the plants. Soluble phosphorus might also be lost from the vegetation residues on the grass buffer strips in the same way. 573 Research Note Research Note References Ahola, H. 1990. Vegetated buffer zone examinations on the Vantaa River basin. Aqua Fennica 20: 65-69. Dillaha.t.a., Reneau R.8., mostaghimui, S. & Lee, D. 1989. Vegetative filter strips for agricultural nonpoint source pollution control. Transactions of the ASAE 32: 513-519. Ekholm, P. 1992. Maataloudesta peräisin oleva fosfori vesien rehevöittäjänä. In: Rekolainen, S. & Kauppi, L. (eds.). Maatalous ja vesien kuormitus. Yhteistut- kimusprojektin tutkimusraportit. Vesi- jaympäristöhalli- tuksen monistesarja No 359. Helsinki, p. 39-46. , Yli-Halla, M. & Kylmälä, P. 1991. Availability of phosphorus in suspended sediments estimated by chem- ical extraction and bioassay. Verb. Internat. Verein. Lim- nol. 24: 2994-2998. Ilmatieteen laitos 1990. Kuukausikatsaus Suomen ilmastoon. Nos 8-12. Helsinki. Ilmatieteen laitos 1991. Kuukausikatsaus Suomen ilmastoon. Nos 1-5, 9-12. Helsinki. Ilmatieteen laitos 1992. Kuukausikatsaus Suomen ilmastoon. Nos 1-4. Helsinki. Magette,W. L., Brinsfield, R. B ..Palmer, R. E., Moon J. D., Dillaha, T. A. & Reneau, R. B. 1987. Vegetated filter strips for agricultural runoff treatment. CBP/TRS 2/87. 125p. U. S. Environmental Protection Agency. Mansikkaniemi,H, 1982. Soil erosion in areas of intensive cultivation in southwestern Finland. Fennia 160: 225- 276. Puustinen, M. 1992. Peltoviljelyksestä aiheutuvan vesistö- kuormituksen vähentäminen. In: Rekolainen, S, & Kauppi, L. (eds.). Maatalous ja vesien kuormitus. Yhteis- tutkimusprojektin tutkimusraportit. Vesi- ja ym- päristöhallituksen monistesarja No 359. Helsinki, p. 107- 121. Rekolainen, S. 1989. Phoshorus and nitrogen load from forest and agricultural areas in Finland. Aqua Fennica 19: 95-107. SFS 3025 Veden fosfaatin määritys. (Finnish standard con- cerning determination of phosphate in water). Suomen standardisoimisliitto. Helsinki 1986. 10p. SFS 3026 Veden kokonaisfosforin määritys. Hajotus perok- sodisulfaatilla. (Finnish standard concerning detetermi- nation of total phosphorus in water. Digestion with per- oxodisulphate). Suomen standardisoimisliitto. Helsinki 1986. 11 p. SFS 3030 Veden nitriitti- ja nitraattitypen summan määritys. (Finnish standard concerning determination of the sum of nitrite and nitrate nitrogen in water). Suomen standardi- soimisliitto. Helsinki 1990. 5 p. SFS 3031 Veden typen määritys, Peroksodisulfaattihapetus. (Finnish standard concerning determination of nitrogen in water. Oxidation with peroxodisulfate). Suomen standardisoimisliitto. Helsinki 1990.6p. SFS 3032. Veden ammoniumtypen määritys. (Finnish stand- ard concerning determination of ammonia-nitrogen of water). Suomen standardisoimisliitto. Helsinki 1976.6 p. Turtola, E. 1990. Minskning av utlakning genom grön- träda. Nordisk jordbruksforskning72: 200. & Jaakkola, A. 1985. Viljelykasvin ja lannoitustason vaikutus typen ja fosforin huuhtoutumiseen savimaasta. Maatalouden tutkimuskeskus. Tiedote 6/85. 43 p. Manuscript received September 1992 Jaana Uusi-Kämppä Toivo Yläranta Agricultural Research Centre of Finland Institute of Soils and Environment SF-31600 Jokioinen, Finland 574 Agric. Sei. Fin!. 1 (1992) Agric. Sei. Fin!. 1 (1992) SELOSTUS Suojakaistat eroosion Ja ravinnehuuhtoutumien vähentäjinä rantapelloilla Jaana Uusi-Kämppä jaToivo Yläranta Maatalouden tutkimuskeskus Maatalouden tutkimuskeskuksessa Jokioisissa aloitettiin suojakaistatutkimus syksyllä 1991. Koekenttä perustettiin savimaalle. Kentän yläosa on melko tasainen, mutta suo- jakaistat ovat rinteessä, jonka keskikaltevuus on 16 %. En- simmäisenä koevuonna selvitettiin 10 m leveän nurmikaistan (kylvetty timotei-nurminata) kykyä estää eroosiota ja ravin- teiden huuhtoutumista pellolta. Suojakaistaruutujen valuma- tuloksia verrattiin ilman suojakaistaa viljeltyihin viljaruutui- hin. Valumavesistä mitattiin kokonaisfosfori, liu-koinen fos- faattifosfori, kokonaistyppi, nitraattityppi, ammoniumtyppi ja haihdutusjäännös, joka kuvasi eroosion suuruutta. Valu- mavesien keräys alkoi syksyllä 1991 puinnin jälkeen ja lop- pui keväällä 1992 valunnan loputtua.Kesällä ei kerätty valu- mavesiä, koska valunta oli hyvin vähäistä. Suojakaistakokeen ensimmäisen koevuoden tulokset osoittavat, että nurmikaistat vähensivät 47 % kokonais- typen, 51 % nitraattitypen, 6 % kokonaisfosforin ja 23 % eroosioaineksen huuhtoutumista. Nurmikaistat puhdistivat pintavaluntavesiä parhaiten syksyllä. Tällöin kokonais- typestä jäi 75 %, nitraattitypestä 79 %, kokonaisfosforista 33 % ja eroosioaineksesta 49 % nurmikaistoille. Keväällä kaistat pidättivät epäpuhtauksia huonommin. Tällöin eroosioaineksen ja fosforin huuhtoutuminen oli nurmikais- toilla suurempaa kuin ilman suojakaistaa viljellyillä ruuduilla. Liukoisen fosforin huuhtoutumisen lisääntymisen syynä saattoi olla nurmikaistojen kasvillisuuteen ja maahan pidättyneen fosforin muuttuminen liukoiseen muotoon keväällä. 575 Research Note